
Well its a historical manhwa where siblings/cousins from the royal bloodline married to keep the royal blood. Also everyone knows Hari is adopted and they are not related by blood, so the general public accepts it (even the villainess Lady Cardis doesnt say anything about that and comments smth like well they are not related by blood and have the right to love each other)

Well thought out.
Eugene is my pick for ml because their relationship is the most interesting potential romance.
I'd also hook up 2nd bro with the guy with teal hair because that would be a fun dynamic.
But I can definitely see why it makes people uncomfortable. I'm also wondering how it's going to play out.

The April Fools chapter of Who Made Me A Princess gave all the homophobes a heart attack. So I imagine it would take a pretty gutsy author to hook up two characters who weren't screaming 'gay' every 5 seconds as a secondary pairing. So even though the best/most interesting match for a failed ml is usually another dude, I always know they're not going there.
Honestly, I like Eugene x Hari.
But it's understandable how people may get uncomfortable by that. If you see it as the other characters being third wheels in this case (her other brothers, any other nobles), then it will be really strange to see them marry eventhough they were somehow known as sister-brother.
It's not a problem in the relationship itself but more about the public opinion. How will they be able to marry without being seen badly by the society? I don't know what kind of setting is this world but in the european noble history, wedding between sisters and brothers wasn't so common (blood related or not). So consequently, there will be an arc about the public opinion too. We can already see the hardship they will need to pass to be able to be together.
That's why, eventhough I like Eugene x Hari, I can agree to people who think it is uncomfortable.